1. Field of the Invention
This document relates to an error diffusion method and a liquid crystal display (LCD) using the same.
2. Discussion of the Related Art
A liquid crystal display (LCD) has the characteristics of being light and thin and driven with low power consumption, so its application coverage is extending. A transmission type LCD, which is the most common LCD, displays an image by modulating light made incident from a backlight unit by controlling an electric field applied to a liquid crystal layer.
A quantization error may be generated in a process of quantizing pixel data of the LCD. An error diffusion method is performed to diffuse a quantization error, which is generated in the quantization process, to pixels which have not been quantized yet among other pixels therearound, to spread the quantization error. A phenomenon that quantization errors collectively appear at portions can be prevented by using the error diffusion method.
Distortion in the form of a contour that may appear in correcting pixel data in the LCD is generated as the portions having a great deal of quantization errors linearly gather. Such linear distortion can be improved by using a method of diffusing a quantization error to nearby pixels, as a quantization method.
In the error diffusion method, the quantization error of pixel data is diffused to nearby pixels by shifting an error diffusion mask as shown in FIG. 1 according to a quantization processing order by using such a method as shown in FIG. 2. The quantization error generated from pixel data which is being currently quantized is diffused to the nearby pixels suitably according to the form and size of a mask as shown in FIG. 1. An error diffusion coefficient of the error diffusion mask illustrated in FIG. 1 is a Floyd-Steinberg error diffusion coefficient.
The error diffusion method requires processing results of previous pixel data in processing the pixel data being currently quantized. Thus, quantization of pixels must be sequentially performed.
When image data inputted to an image display device includes only one pixel data at every clock through one port input, there is no problem with application of the error diffusion method. However, if two or more pixel data are simultaneously inputted to the LCD at every clock through two ports or n number of port input terminals (n is a positive integer larger than 2), two or more of pixel data are simultaneously quantized at every clock. Thus, the related art error diffusion method can be applicable for only one port input, not for the n number of port inputs.
The recent LCD has improved contrast through a local dimming method in which an input image is analyzed and light sources are turned on by blocks. In the local dimming method, a backlight is divided into a plurality of blocks, and the luminance of the blocks where an image is brighter in the backlight is increased while the luminance of the blocks where an image is relatively dark in the backlight is lowered. Because the light sources are turned on by the blocks, namely, partially turned on, the luminance of the backlight employing the local dimming method is lower than the luminance of a backlight in which the entire light sources are turned on without using local dimming. Thus, in order to compensate the low backlight luminance of the local dimming method, pixel data may be compensated for. In this case, however, light density of the backlight has an analog level (infinite resolution), while the pixel data is digital data having a determined bit width, so when the pixel data is compensated for in case of local dimming, a quantization error may be generated. Thus, an error diffusion method needs to be applied in case of compensating for the pixel data in case of local dimming.